1. Field of Invention
The present invention relates to a direct current light emitting device control circuit with a dimming function and a method thereof, in particular to such direct current light emitting device control circuit with a dimming function which has a better power factor because it does not need to use a tri-electro AC switch (hereinafter referred to as the “TRIAC device”), and a method thereof.
2. Description of Related Art
LEDs (light emitting diodes) are one typical type of direct current light emitting devices. Referring to FIG. 1, in prior art, to drive the LEDs from an AC power source, the AC power is first rectified by a bridge rectifier 4, and the rectified AC power is converted to a DC voltage by an AC-DC power regulator 10; next, an LED driver circuit 20 operates according to the DC voltage to control the currents of the LEDs. The AC-DC power regulator 10 includes a primary side circuit 11, a secondary side circuit 12, a transformer 13, and other discrete devices such as capacitors and diodes (not shown). The secondary side circuit 12 detects the output voltage and the detection result is fed back to the switch control circuit PWM in the primary side circuit 11 by opto-coupling, to control the operation of the power switch P of the primary side circuit 11.
The drawback of the foregoing prior art is that it requires the AC-DC power regulator 10 to generate a regulated voltage, and the LED driver circuit 20 to control the currents of the LEDs according to the voltage, so at least three integrated circuit (IC) chips are needed: the primary side circuit 11, the secondary side circuit 12, and the LED driver circuit 20; the cost is high for such an arrangement.
In addition, as an AC power source is used, if it is required to adjust the brightness (i.e., dimming) of the light emitting devices, the prior art usually utilizes a tri-electro AC switch (TRIAC) device 2 as shown in FIG. 2 to extract the turn-ON angle of the inputted AC power, so as to adjust the output power for achieving the dimming function. However, one major disadvantage of using the TRIAC device is that it degrades the power factor because it changes the turn-ON angle.
In view of above, the present invention overcomes the foregoing drawbacks by putting forth a direct current light emitting device control circuit with a dimming function and a corresponding method, which utilize a novel dimming control mechanism rather than a TRIAC device, so that the power factor is better and the power consumption is reduced.